Competitive adsorption of multiple proteins to nanoparticles: the Vroman effect revisited

Nanoparticle Isolation from Biological Media for Protein Corona Analysis: The Impact of Incubation and Recovery Protocols on Nanoparticle Properties

Nanoparticles are increasingly implemented in biomedical applications, including the diagnosis and treatment of disease. When exposed to complex biological media, nanoparticles spontaneously interact with their surrounding environment, leading to the surface-adsorption of small and bio- macromolecules- termed the "corona". Corona composition is governed by nanoparticle properties and incubation parameters. While the focus of most studies is on the protein signature of the nanoparticle corona, the impact of experimental protocols on nanoparticle size in the presence of complex biological media, and the impact of nanoparticle recovery from biological media has not yet been reported. Here using a non-degradable robust model, we show how centrifugation-resuspension protocols used for the isolation of nanoparticles from incubation media, incubation duration and shear flow conditions alter nanoparticle parameters including particle size, zeta potential and total protein content. Our results show significant changes in nanoparticle size following exposure to media containing protein under different flow conditions, which also altered the composition of surface-adsorbed proteins profiled by SDS-PAGE. Our in situ analysis of nanoparticle size in media containing protein using particle tracking analysis highlights that centrifugation-resuspension is disruptive to agglomerates that are spontaneously formed in protein containing media, highlighting the need for in situ analytical methods that do not alter the intermediates formed following nanoparticle exposure to biological media. Nanomedicines are mostly intended for parenteral administration, and our findings show that parameters such as shear flow can significantly alter nanoparticle physicochemical parameters. Overall, we show that the centrifugation-resuspension isolation of nanoparticles from media significantly alters particle parameters in addition to the overall protein composition of surface-adsorbed proteins. We recommend that nanoparticle characterization pipelines studying bio-nano interactions during early nanomedicine development consider biologically-relevant shear flow conditions and media composition that can significantly alter particle physical parameters and subsequent conclusions from these studies.

Label free tracking to quantify nanoparticle diffusion through biological media

Nanotechnology is a rapidly evolving field and has been extensively studied in biological applications. An understanding of the factors that influence nanoparticle diffusion in biofluids can aid in the development of diverse technologies. The development of real-time, label-free tracking technologies would allow the expansion of current knowledge of the diffusion and activity of nanoparticles. Fluorescence-based microscopy is one of the most widespread tools to monitor and track nanoparticle dynamics; however, the influence of fluorescent tags on diffusion and biological activity is still unclear. In this study, we experimentally determined the diffusion coefficient of gold nanoparticles using a label-free, optical tracking technique and evaluated the influence of protein concentration, charge and diameter on nanoparticle diffusion through biological media. We dispersed positively- and negatively-charged nanoparticles with diameters varying from 10 to 100 nm in a common cell culture media with different concentrations of serum proteins. Our results show that dynamic protein interactions influence nanoparticle diffusion in the range of serum concentrations tested. Experimental regimes to obtain quantitative information on the factors that influence the dynamics of nanoparticles in biological media have been developed.

Looking back, moving forward: protein corona of lipid nanoparticles

Lipid nanoparticles (LNPs) are commonly employed for drug delivery owing to their considerable drug-loading capacity, low toxicity, and excellent biocompatibility. Nevertheless, the formation of protein corona (PC) on their surfaces significantly influences the drug's in vivo fate (such as absorption, distribution, metabolism, and elimination) upon administration. PC denotes the phenomenon wherein one or multiple strata of proteins adhere to the external interface of nanoparticles (NPs) or microparticles within the biological milieu, encompassing ex vivo fluids (e.g., serum-containing culture media) and in vivo fluids (such as blood and tissue fluids). Hence, it is essential to claim the PC formation behaviors and mechanisms on the surface of LNPs. This overview provided a comprehensive examination of crucial aspects related to such issues, encompassing time evolution, controllability, and their subsequent impacts on LNPs. Classical studies of PC generation on the surface of LNPs were additionally integrated, and its decisive role in shaping the in vivo fate of LNPs was explored. The mechanisms underlying PC formation, including the adsorption theory and alteration theory, were introduced to delve into the formation process. Subsequently, the existing experimental outcomes were synthesized to offer insights into the research and application facets of PC, and it was concluded that the manipulation of PC held substantial promise in the realm of targeted delivery.

Modulating the toxicity of engineered nanoparticles by controlling protein corona formation: Recent advances and future prospects

With the rapid development and widespread application of engineered nanoparticles (ENPs), understanding the fundamental interactions between ENPs and biological systems is essential to assess and predict the fate of ENPs in vivo. When ENPs are exposed to complex physiological environments, biomolecules quickly and inevitably adsorb to ENPs to form a biomolecule corona, such as a protein corona (PC). The formed PC has a significant effect on the physicochemical properties of ENPs and gives them a brand new identity in the biological environment, which determines the subsequent ENP-cell/tissue/organ interactions. Controlling the formation of PCs is therefore of utmost importance to accurately predict and optimize the behavior of ENPs within living organisms, as well as ensure the safety of their applications. In this review, we provide an overview of the fundamental aspects of the PC, including the formation mechanism, composition, and frequently used characterization techniques. We comprehensively discuss the potential impact of the PC on ENP toxicity, including cytotoxicity, immune response, and so on. Additionally, we summarize recent advancements in manipulating PC formation on ENPs to achieve the desired biological outcomes. We further discuss the challenges and prospects, aiming to provide valuable insights for a better understanding and prediction of ENP behaviors in vivo, as well as the development of low-toxicity ENPs.

Multiscale modelling of biomolecular corona formation on metallic surfaces

In the realm of food industry, the choice of non-consumable materials used plays a crucial role in ensuring consumer safety and product quality. Aluminum is widely used in food packaging and food processing applications, including dairy products. However, the interaction between aluminum and milk content requires further investigation to understand its implications. In this work, we present the results of multiscale modelling of the interaction between various surfaces, that is (100), (110), and (111), of fcc aluminum with the most abundant milk proteins and lactose. Our approach combines atomistic molecular dynamics, a coarse-grained model of protein adsorption, and kinetic Monte Carlo simulations to predict the protein corona composition in the deposited milk layer on aluminum surfaces. We consider a simplified model of milk, which is composed of the six most abundant milk proteins found in natural cow milk and lactose, which is the most abundant sugar found in dairy. Through our study, we ranked selected proteins and lactose adsorption affinities based on their corresponding interaction strength with aluminum surfaces and predicted the content of the naturally forming biomolecular corona. Our comprehensive investigation sheds light on the implications of aluminum in food processing and packaging, particularly concerning its interaction with the most abundant milk proteins and lactose. By employing a multiscale modelling approach, we simulated the interaction between metallic aluminum surfaces and the proteins and lactose, considering different crystallographic orientations. The results of our study provide valuable insights into the mechanisms of lactose and protein deposition on aluminum surfaces, which can aid in the general understanding of protein corona formation.

Review of Advances in Coating and Functionalization of Gold Nanoparticles: From Theory to Biomedical Application

Nanoparticles, especially gold nanoparticles (Au NPs) have gained increasing interest in biomedical applications. Used for disease prevention, diagnosis and therapies, its significant advantages in therapeutic efficacy and safety have been the main target of interest. Its application in immune system prevention, stability in physiological environments and cell membranes, low toxicity and optimal bioperformances are critical to the success of engineered nanomaterials. Its unique optical properties are great attractors. Recently, several physical and chemical methods for coating these NPs have been widely used. Biomolecules such as DNA, RNA, peptides, antibodies, proteins, carbohydrates and biopolymers, among others, have been widely used in coatings of Au NPs for various biomedical applications, thus increasing their biocompatibility while maintaining their biological functions. This review mainly presents a general and representative view of the different types of coatings and Au NP functionalization using various biomolecules, strategies and functionalization mechanisms.

Competition of opsonins and dysopsonins on the nanoparticle surface

The biological behavior and fate of nanoparticles are dependent on their retention time in the blood circulation system. The protein corona components, especially opsonins, and dysopsonins, adsorbed on the nanoparticle surface determine their blood circulation time. The protein corona formation is a dynamic process that involves the competition between different proteins to be adsorbed on the nanoparticles. Therefore, studying how proteins compete and are oriented on the nanoparticle surface is essential. We hypothesized that the presence of opsonins (immunoglobulin (IgG)) might affect the adsorption of dysopsonins (human serum albumin (HSA)) and vice versa. Using the molecular dynamics simulations, we showed that the adsorption of HSA on the GO surface after the IgG adsorption is more probable than the opposite order of adsorption. It was also observed that the higher lateral diffusion of the HSA compared to the IgG helped the system reach a more stable configuration while the initial adsorption of the HSA limits the lateral diffusion of IgG. Therefore, replacing IgG adsorbed on the GO surface with HSA is plausible while the reverse process is less likely to occur. This study revealed that albumin might extend the blood circulation time of GO by replacing opsonins (IgG).

Polymeric Nanoparticles and Nanogels: How Do They Interact with Proteins?

Polymeric nanomaterials, nanogels, and solid nanoparticles can be fabricated using single or double emulsion methods. These materials hold great promise for various biomedical applications due to their biocompatibility, biodegradability, and their ability to control interactions with body fluids and cells. Despite the increasing use of nanoparticles in biomedicine and the plethora of publications on the topic, the biological behavior and efficacy of polymeric nanoparticles (PNPs) have not been as extensively studied as those of other nanoparticles. The gap between the potential of PNPs and their applications can mainly be attributed to the incomplete understanding of their biological identity. Under physiological conditions, such as specific temperatures and adequate protein concentrations, PNPs become coated with a "protein corona" (PC), rendering them potent tools for proteomics studies. In this review, we initially investigate the synthesis routes and chemical composition of conventional PNPs to better comprehend how they interact with proteins. Subsequently, we comprehensively explore the effects of material and biological parameters on the interactions between nanoparticles and proteins, encompassing reactions such as hydrophobic bonding and electrostatic interactions. Moreover, we delve into recent advances in PNP-based models that can be applied to nanoproteomics, discussing the new opportunities they offer for the clinical translation of nanoparticles and early prediction of diseases. By addressing these essential aspects, we aim to shed light on the potential of polymeric nanoparticles for biomedical applications and foster further research in this critical area.

Milk Protein Adsorption on Metallic Iron Surfaces

Food processing and consumption involves multiple contacts between biological fluids and solid materials of processing devices, of which steel is one of the most common. Due to the complexity of these interactions, it is difficult to identify the main control factors in the formation of undesirable deposits on the device surfaces that may affect safety and efficiency of the processes. Mechanistic understanding of biomolecule-metal interactions involving food proteins could improve management of these pertinent industrial processes and consumer safety in the food industry and beyond. In this work, we perform a multiscale study of the formation of protein corona on iron surfaces and nanoparticles in contact with cow milk proteins. By calculating the binding energies of proteins with the substrate, we quantify the adsorption strength and rank proteins by the adsorption affinity. We use a multiscale method involving all-atom and coarse-grained simulations based on generated ab initio three-dimensional structures of milk proteins for this purpose. Finally, using the adsorption energy results, we predict the composition of protein corona on iron curved and flat surfaces via a competitive adsorption model.

Mechanistic Understanding of Protein Corona Formation around Nanoparticles: Old Puzzles and New Insights

Although a wide variety of nanoparticles (NPs) have been engineered for use as disease markers or drug delivery agents, the number of nanomedicines in clinical use has hitherto remained small. A key obstacle in nanomedicine development is the lack of a deep mechanistic understanding of NP interactions in the bio-environment. Here, the focus is on the biomolecular adsorption layer (protein corona), which quickly enshrouds a pristine NP exposed to a biofluid and modifies the way the NP interacts with the bio-environment. After a brief introduction of NPs for nanomedicine, proteins, and their mutual interactions, research aimed at addressing fundamental properties of the protein corona, specifically its mono-/multilayer structure, reversibility and irreversibility, time dependence, as well as its role in NP agglomeration, is critically reviewed. It becomes quite evident that the knowledge of the protein corona is still fragmented, and conflicting results on fundamental issues call for further mechanistic studies. The article concludes with a discussion of future research directions that should be taken to advance the understanding of the protein corona around NPs. This knowledge will provide NP developers with the predictive power to account for these interactions in the design of efficacious nanomedicines.

Comparative study of force-based classical density functional theory

We reexamine results obtained with the recently proposed density functional theory framework based on forces (force-DFT) [S. M. Tschopp et al., Phys. Rev. E 106, 014115 (2022)2470-004510.1103/PhysRevE.106.014115]. We compare inhomogeneous density profiles for hard sphere fluids to results from both standard density functional theory and from computer simulations. Test situations include the equilibrium hard sphere fluid adsorbed against a planar hard wall and the dynamical relaxation of hard spheres in a switched harmonic potential. The comparison to grand canonical Monte Carlo simulation profiles shows that equilibrium force-DFT alone does not improve upon results obtained with the standard Rosenfeld functional. Similar behavior holds for the relaxation dynamics, where we use our event-driven Brownian dynamics data as benchmark. Based on an appropriate linear combination of standard and force-DFT results, we investigate a simple hybrid scheme which rectifies these deficiencies in both the equilibrium and the dynamical case. We explicitly demonstrate that although the hybrid method is based on the original Rosenfeld fundamental measure functional, its performance is comparable to that of the more advanced White Bear theory.

A proteome scale study reveals how plastic surfaces and agitation promote protein aggregation

Protein aggregation in biotherapeutics can reduce their activity and effectiveness. It may also promote immune reactions responsible for severe adverse effects. The impact of plastic materials on protein destabilization is not totally understood. Here, we propose to deconvolve the effects of material surface, air/liquid interface, and agitation to decipher their respective role in protein destabilization and aggregation. We analyzed the effect of polypropylene, TEFLON, glass and LOBIND surfaces on the stability of purified proteins (bovine serum albumin, hemoglobin and α-synuclein) and on a cell extract composed of 6000 soluble proteins during agitation (P = 0.1-1.2 W/kg). Proteomic analysis revealed that chaperonins, intrinsically disordered proteins and ribosomes were more sensitive to the combined effects of material surfaces and agitation while small metabolic oligomers could be protected in the same conditions. Protein loss observations coupled to Raman microscopy, dynamic light scattering and proteomic allowed us to propose a mechanistic model of protein destabilization by plastics. Our results suggest that protein loss is not primarily due to the nucleation of small aggregates in solution, but to the destabilization of proteins exposed to material surfaces and their subsequent aggregation at the sheared air/liquid interface, an effect that cannot be prevented by using LOBIND tubes. A guidance can be established on how to minimize these adverse effects. Remove one of the components of this combined stress - material, air (even partially), or agitation - and proteins will be preserved.

Bio- and eco-corona related to plants: Understanding the formation and biological effects of plant protein coatings on nanoparticles

The thriving nano-enabled agriculture facilitates the interaction of nanomaterials with plants. Recently, these interactions and their biological effects are receiving increasing attention. Upon entering plants via leaves, roots, stems, and other organs, nanoparticles adsorb numerous biomolecules inside plants and form bio-corona. In addition, nanoparticles that enter plants through roots may have formed eco-corona with root exudates in the rhizosphere environment before contacting with plant exogenous proteins. The most significant biological effects of plant protein corona include changes in protein structure and function, as well as changes in nanoparticle toxicity and targeting ability. However, the mechanisms, particularly how protein corona affects plant protein function, plant development and growth, and rhizosphere environment properties, require further investigation. Our review summarizes the current understanding of the formation and biological effects of nanoparticle-plant protein corona and provides an outlook on future research.

Hemolytic Activity of Nanoparticles as a Marker of Their Hemocompatibility

The potential use of nanomaterials in medicine offers opportunities for novel therapeutic approaches to treating complex disorders. For that reason, a new branch of science, named nanotoxicology, which aims to study the dangerous effects of nanomaterials on human health and on the environment, has recently emerged. However, the toxicity and risk associated with nanomaterials are unclear or not completely understood. The development of an adequate experimental strategy for assessing the toxicity of nanomaterials may include a rapid/express method that will reliably, quickly, and cheaply make an initial assessment. One possibility is the characterization of the hemocompatibility of nanomaterials, which includes their hemolytic activity as a marker. In this review, we consider various factors affecting the hemolytic activity of nanomaterials and draw the reader's attention to the fact that the formation of a protein corona around a nanoparticle can significantly change its interaction with the red cell. This leads us to suggest that the nanomaterial hemolytic activity in the buffer does not reflect the situation in the blood plasma. As a recommendation, we propose studying the hemocompatibility of nanomaterials under more physiologically relevant conditions, in the presence of plasma proteins in the medium and under mechanical stress.

A Nanomedicine Structure-Activity Framework for Research, Development, and Regulation of Future Cancer Therapies

Despite their clinical success in drug delivery applications, the potential of theranostic nanomedicines is hampered by mechanistic uncertainty and a lack of science-informed regulatory guidance. Both the therapeutic efficacy and the toxicity of nanoformulations are tightly controlled by the complex interplay of the nanoparticle's physicochemical properties and the individual patient/tumor biology; however, it can be difficult to correlate such information with observed outcomes. Additionally, as nanomedicine research attempts to gradually move away from large-scale animal testing, the need for computer-assisted solutions for evaluation will increase. Such models will depend on a clear understanding of structure-activity relationships. This review provides a comprehensive overview of the field of cancer nanomedicine and provides a knowledge framework and foundational interaction maps that can facilitate future research, assessments, and regulation. By forming three complementary maps profiling nanobio interactions and pathways at different levels of biological complexity, a clear picture of a nanoparticle's journey through the body and the therapeutic and adverse consequences of each potential interaction are presented.

Phenol release from pNIPAM hydrogels: scaling molecular dynamics simulations with dynamical density functional theory

We employed molecular dynamic simulations (MD) and the Bennett's acceptance ratio method to compute the free energy of transfer, ΔG_trans, of phenol, methane, and 5-fluorouracil (5-FU), between bulk water and water-pNIPAM mixtures of different polymer volume fractions, ϕ_p. For this purpose, we first calculate the solvation free energies in both media to obtain ΔG_trans. Phenol and 5-FU (a medication used to treat cancer) attach to the pNIPAM surface so that they show negative values of ΔG_trans irrespective of temperature (above or below the lower critical solution temperature of pNIPAM, T_c). Conversely, methane switches the ΔG_trans sign when considering temperatures below (positive) and above (negative) T_c. In all cases, and contrasting with some theoretical predictions, ΔG_trans maintains a linear behavior with the pNIPAM concentration up to large polymer densities. We have also employed MD to compute the diffusion coefficient, D, of phenol in water-pNIPAM mixtures as a function of ϕ_p in the diluted limit. Both ΔG_trans and D as a function of ϕ_p are required inputs to obtain the release halftime of hollow pNIPAM microgels through Dynamic Density Functional Theory (DDFT). Our scaling strategy captures the experimental value of 2200 s for 50 μm radius microgels with no cavity, for ϕ_p ≃ 0.83 at 315 K.

Cell-membrane-inspired polymers for constructing biointerfaces with efficient molecular recognition

Fabrication of devices that accurately recognize, detect, and separate target molecules from mixtures is a crucial aspect of biotechnology for applications in medical, pharmaceutical, and food sciences. This technology has also been recently applied in solving environmental and energy-related problems. In molecular recognition, biomolecules are typically complexed with a substrate, and specific molecules from a mixture are recognized, captured, and reacted. To increase sensitivity and efficiency, the activity of the biomolecules used for capture should be maintained, and non-specific reactions on the surface should be prevented. This review summarizes polymeric materials that are used for constructing biointerfaces. Precise molecular recognition occurring at the surface of cell membranes is fundamental to sustaining life; therefore, materials that mimic the structure and properties of this particular surface are emphasized in this article. The requirements for biointerfaces to eliminate nonspecific interactions of biomolecules are described. In particular, the major issue of protein adsorption on biointerfaces is discussed by focusing on the structure of water near the interface from a thermodynamic viewpoint; moreover, the structure of polymer molecules that control the water structure is considered. Methodologies enabling stable formation of these interfaces on material surfaces are also presented.

Dynamic process, mechanisms, influencing factors and study methods of protein corona formation

Nanoparticles interacting with proteins to form protein corona represent one of the most fundamental problems in the rapid development of nanotechnology. In the past decade, thousands of studies have pointed out this issue. Within multi-protein systems, the formation of protein corona is a homeostasis process in which proteins compete for the limited surface sites of nanoparticles. Besides, the formation of protein corona generally shows a tendency of evolving with time and involves many different driving forces controlled by properties of nanoparticles, proteins and environment. Therefore, recent research on the dynamic process and mechanisms of protein corona formation in both animals and plants are summarized in this review. The factors that affect the formation and the techniques that commonly used for protein corona analysis are proposed. Furthermore, in order to provide reference for the future research, the limitations and challenges in protein corona studies are assessed and the future perspectives are proposed.

Particle Safety Assessment in Additive Manufacturing: From Exposure Risks to Advanced Toxicology Testing

Additive manufacturing (AM) or industrial three-dimensional (3D) printing drives a new spectrum of design and production possibilities; pushing the boundaries both in the application by production of sophisticated products as well as the development of next-generation materials. AM technologies apply a diversity of feedstocks, including plastic, metallic, and ceramic particle powders with distinct size, shape, and surface chemistry. In addition, powders are often reused, which may change the particles' physicochemical properties and by that alter their toxic potential. The AM production technology commonly relies on a laser or electron beam to selectively melt or sinter particle powders. Large energy input on feedstock powders generates several byproducts, including varying amounts of virgin microparticles, nanoparticles, spatter, and volatile chemicals that are emitted in the working environment; throughout the production and processing phases. The micro and nanoscale size may enable particles to interact with and to cross biological barriers, which could, in turn, give rise to unexpected adverse outcomes, including inflammation, oxidative stress, activation of signaling pathways, genotoxicity, and carcinogenicity. Another important aspect of AM-associated risks is emission/leakage of mono- and oligomers due to polymer breakdown and high temperature transformation of chemicals from polymeric particles, both during production, use, and in vivo, including in target cells. These chemicals are potential inducers of direct toxicity, genotoxicity, and endocrine disruption. Nevertheless, understanding whether AM particle powders and their byproducts may exert adverse effects in humans is largely lacking and urges comprehensive safety assessment across the entire AM lifecycle-spanning from virgin and reused to airborne particles. Therefore, this review will detail: 1) brief overview of the AM feedstock powders, impact of reuse on particle physicochemical properties, main exposure pathways and protective measures in AM industry, 2) role of particle biological identity and key toxicological endpoints in the particle safety assessment, and 3) next-generation toxicology approaches in nanosafety for safety assessment in AM. Altogether, the proposed testing approach will enable a deeper understanding of existing and emerging particle and chemical safety challenges and provide a strategy for the development of cutting-edge methodologies for hazard identification and risk assessment in the AM industry.

Protein adsorption onto nanomaterials engineered for theranostic applications

The key role of biomolecule adsorption onto engineered nanomaterials for therapeutic and diagnostic purposes has been well recognized by the nanobiotechnology community, and our mechanistic understanding of nano-bio interactions has greatly advanced over the past decades. Attention has recently shifted to gaining active control of nano-bio interactions, so as to enhance the efficacy of nanomaterials in biomedical applications. In this review, we summarize progress in this field and outline directions for future development. First, we briefly review fundamental knowledge about the intricate interactions between proteins and nanomaterials, as unraveled by a large number of mechanistic studies. Then, we give a systematic overview of the ways that protein-nanomaterial interactions have been exploited in biomedical applications, including the control of protein adsorption for enhancing the targeting efficiency of nanomedicines, the design of specific protein adsorption layers on the surfaces of nanomaterials for use as drug carriers, and the development of novel nanoparticle array-based sensors based on nano-bio interactions. We will focus on particularly relevant and recent examples within these areas. Finally, we conclude this topical review with an outlook on future developments in this fascinating research field.

Flummoxed by flux: the indeterminate principles of haemodialysis

In haemodialysis (HD), unwanted substances (uraemic retention solutes or ‘uraemic toxins’) that accumulate in uraemia are removed from blood by transport across the semipermeable membrane. Like all membrane separation processes, the transport requires driving forces to facilitate the transfer of molecules across the membrane. The magnitude of the transport is quantified by the phenomenon of ‘flux’, a finite parameter defined as the volume of fluid (or permeate) transferred per unit area of membrane surface per unit time. In HD, as transmembrane pressure is applied to facilitate fluid flow or flux across the membrane to enhance solute removal, flux is defined by the ultrafiltration coefficient (KUF; mL/h/mmHg) reflecting the hydraulic permeability of the membrane. However, in HD, the designation of flux has come to be used in a much broader sense and the term is commonly used interchangeably and erroneously with other measures of membrane separation processes, resulting in considerable confusion. Increased flux is perceived to reflect more ‘porous’ membranes having ‘larger’ pores, even though other membrane and therapy attributes determine the magnitude of flux achieved during HD. Adjectival designations of flux (low-, mid-, high-, super-, ultra-) have found indiscriminate usage in the scientific literature to qualify a parameter that influences clinical decision making and prescription of therapy modalities (low-flux or high-flux HD). Over the years the concept and definition of flux has undergone arbitrary and periodic adjustment and redefinition by authors in publications, regulatory bodies (US Food and Drug Administration) and professional association guidelines (European Renal Association, Kidney Disease Outcomes Quality Initiative), with little consensus. Industry has stretched the boundaries of flux to derive marketing advantages, justify increased reimbursement or contrive new classes of therapy modalities when in fact flux is just one of several specifications that determine membrane or dialyser performance. Membranes considered as high-flux previously are today at the lower end of the flux spectrum. Further, additional parameters unrelated to the rate of diffusive or convective transport (flux) are used in conjunction with or in place of KUF to allude to flux: clearance (mL/min, e.g. of β₂-microglobulin) or sieving coefficients (dimensionless). Considering that clinical trials in nephrology, designed to make therapy recommendations and guide policy with economic repercussions, are based on the parameter flux they merit clarification—by regulatory authorities and scientists alike—to avoid further misappropriation.

Blood-incompatibility in haemodialysis: alleviating inflammation and effects of coagulation

Blood-incompatibility is an inevitability of all blood-contacting device applications and therapies, including haemodialysis (HD). Blood leaving the environment of blood vessels and the protection of the endothelium is confronted with several stimuli of the extracorporeal circuit (ECC), triggering the activation of blood cells and various biochemical pathways of plasma. Prevention of blood coagulation, a major obstacle that needed to be overcome to make HD possible, remains an issue to contend with. While anticoagulation (mainly with heparin) successfully prevents clotting within the ECC to allow removal of uraemic toxins across the dialysis membrane wall, it is far from ideal, triggering heparin-induced thrombocytopenia in some instances. Soluble fibrin can form even in the presence of heparin and depending on the constitution of the patient and activation of platelets, could result in physical clots within the ECC (e.g. bubble trap chamber) and, together with other plasma and coagulation proteins, result in increased adsorption of proteins on the membrane surface. The buildup of this secondary membrane layer impairs the transport properties of the membrane to reduce the clearance of uraemic toxins. Activation of complement system-dependent immune response pathways leads to leukopenia, formation of platelet–neutrophil complexes and expression of tissue factor contributing to thrombotic processes and a procoagulant state, respectively. Complement activation also promotes recruitment and activation of leukocytes resulting in oxidative burst and release of pro-inflammatory cytokines and chemokines, thereby worsening the elevated underlying inflammation and oxidative stress condition of chronic kidney disease patients. Restricting all forms of blood-incompatibility, including potential contamination of dialysis fluid with endotoxins leading to inflammation, during HD therapies is thus still a major target towards more blood-compatible and safer dialysis to improve patient outcomes. We describe the mechanisms of various activation pathways during the interaction between blood and components of the ECC and describe approaches to mitigate the effects of these adverse interactions. The opportunities to develop improved dialysis membranes as well as implementation strategies with less potential for undesired biological reactions are discussed.

Late stage of the formation of a protein corona around nanoparticles in biofluids

In biofluids containing various proteins, nanoparticles rapidly come to be surrounded by a nanometer-thick protein layer referred to as a protein corona. The late stage of this process occurs via replacement of proteins already bound to a nanoparticle by new ones. In the available kinetic models, this process is considered to include independent acts of protein detachment and attachment. It can, however, occur also at the level of protein pairs via exchange, i.e., concerted replacement of an attached protein by a newly arrived one. I argue that the exchange channel can be more important than the conventional one. To illustrate the likely specifics of the exchange channel, I present a kinetic model focused exclusively on this channel and based on the Evans-Polanyi-type relation between the activation energies of the protein-exchange steps and the protein binding energies. The corresponding kinetics were calculated for three qualitatively different distributions of proteins in solution over binding energy (with a maximum or monotonously decreasing or increasing, respectively) and are found to be similar, with relatively rapid replacement of weakly bound proteins and slow redistribution of strongly bound proteins. The ratio of the timescales characterizing the evolution of weakly and strongly bound proteins is found to depend on the type of the binding-energy distribution.

A 3D Microfluidic ELISA for the Detection of Severe Dengue: Sensitivity Improvement and Vroman Effect Amelioration by EDC-NHS Surface Modification

Serum is commonly used as a specimen in immunoassays but the presence of heterophilic antibodies can potentially interfere with the test results. Previously, we have developed a microfluidic device called: 3D Stack for enzyme-linked immunosorbent assay (ELISA). However, its evaluation was limited to detection from a single protein solution. Here, we investigated the sensitivity of the 3D Stack in detecting a severe dengue biomarker—soluble CD163 (sCD163)—within the serum matrix. To determine potential interactions with serum matrix, a spike-and-recovery assay was performed, using 3D Stacks with and without surface modification by an EDC–NHS (N-ethyl-N′-(3-(dimethylamino)propyl)carbodiimide/N-hydroxysuccinimide) coupling. Without surface modification, a reduced analyte recovery in proportion to serum concentration was observed because of the Vroman effect, which resulted in competitive displacement of coated capture antibodies by serum proteins with stronger binding affinities. However, EDC–NHS coupling prevented antibody desorption and improved the sensitivity. Subsequent comparison of sCD163 detection using a 3D Stack with EDC–NHS coupling and conventional ELISA in dengue patients’ sera revealed a high correlation (R = 0.9298, p < 0.0001) between the two detection platforms. Bland–Altman analysis further revealed insignificant systematic error between the mean differences of the two methods. These data suggest the potentials of the 3D Stack for further development as a detection platform.

A hard-sphere model of protein corona formation on spherical and cylindrical nanoparticles

A nanoparticle (NP) immersed in biological media rapidly forms a corona of adsorbed proteins, which later controls the eventual fate of the particle and the route through which adverse outcomes may occur. The composition and timescale for the formation of this corona are both highly dependent on both the NP and its environment. The deposition of proteins on the surface of the NP can be imitated by a process of random sequential adsorption, and, based on this model, we develop a rate-equation treatment for the formation of a corona represented by hard spheres on spherical and cylindrical NPs. We find that the geometry of the NP significantly alters the composition of the corona through a process independent of the rate constants assumed for adsorption and desorption of proteins, with the radius and shape of the NP both influencing the corona. We further investigate the roles of protein mobility on the surface of the NP and changes in the concentration of proteins.

The five problems of irreversibility

Thermodynamics has a clear arrow of time, characterized by the irreversible approach to equilibrium. This stands in contrast to the laws of microscopic theories, which are invariant under time-reversal. Foundational discussions of this "problem of irreversibility" often focus on historical considerations, and do therefore not take results of modern physical research on this topic into account. In this article, I will close this gap by studying the implications of dynamical density functional theory (DDFT), a central method of modern nonequilibrium statistical mechanics not previously considered in philosophy of physics, for this debate. For this purpose, the philosophical discussion of irreversibility is structured into five problems, concerned with the source of irreversibility in thermodynamics, the definition of equilibrium and entropy, the justification of coarse-graining, the approach to equilibrium and the arrow of time. For each of these problems, it is shown that DDFT provides novel insights that are of importance for both physicists and philosophers of physics.

In vivo protein corona on nanoparticles: does the control of all material parameters orient the biological behavior?

Nanomaterials have a huge potential in research fields from nanomedicine to medical devices. However, surface modifications of nanoparticles (NPs) and thus of their physicochemical properties failed to predict their biological behavior. This requires investigating the "missing link" at the nano-bio interface. The protein corona (PC), the set of proteins binding to the NPs surface, plays a critical role in particle recognition by the innate immune system. Still, in vitro incubation offers a limited understanding of biological interactions and fails to explain the in vivo fate. To date, several reports explained the impact of PC in vitro but its applications in the clinical field have been very limited. Furthermore, PC is often considered as a biological barrier reducing the targeting efficiency of nano vehicles. But the protein binding can actually be controlled by altering PC both in vitro and in vivo. Analyzing PC in vivo could accordingly provide a deep understanding of its biological effect and speed up the transfer to clinical applications. This review demonstrates the need for clarifications on the effect of PC in vivo and the control of its behavior by changing its physicochemical properties. It unfolds the recent in vivo developments to understand mechanisms and challenges at the nano-bio interface. Finally, it reports recent advances in the in vivo PC to overcome and control the limitations of the in vitro PC by employing PC as a boosting resource to prolong the NPs half-life, to improve their formulations and thereby to increase its use for biomedical applications.

Adsorption kinetics and thermodynamic properties of a binary mixture of hard-core particles on a square lattice

The adsorption kinetics and thermodynamic properties of a binary mixture on a square lattice are studied using the random sequential adsorption with surface diffusion (RSAD). We compare the adsorption of binary species with different equilibrium rate constants and effective rates of adsorption to a surface and find that the temporal evolution of surface coverages of both species can be obtained through the use of the blocking function of a system with irreversible adsorption of highly diffusive particles. Binary mixtures, when one of the components follows the random sequential adsorption (RSA) without surface diffusion and the other follows the RSAD model, display competitive adsorption in addition to cooperative phenomena. Specifically, (i) species replacement occurs over a long period of time, while the total coverage remains unchanged after a short time, (ii) the presence of the RSAD component shifts the jamming coverage to the higher values, and (iii) the maximum jamming coverage is obtained when the effective adsorption of the RSA type components is lower than the other adsorbing particles.

Understanding the Interaction of Polyelectrolyte Architectures with Proteins and Biosystems

The counterions neutralizing the charges on polyelectrolytes such as DNA or heparin may dissociate in water and greatly influence the interaction of such polyelectrolytes with biomolecules, particularly proteins. In this Review we give an overview of studies on the interaction of proteins with polyelectrolytes and how this knowledge can be used for medical applications. Counterion release was identified as the main driving force for the binding of proteins to polyelectrolytes: Patches of positive charge become multivalent counterions of the polyelectrolyte and lead to the release of counterions from the polyelectrolyte and a concomitant increase in entropy. This is shown from investigations on the interaction of proteins with natural and synthetic polyelectrolytes. Special emphasis is paid to sulfated dendritic polyglycerols (dPGS). The Review demonstrates that we are moving to a better understanding of charge-charge interactions in systems of biological relevance. Research along these lines will aid and promote the design of synthetic polyelectrolytes for medical applications.

Effects of social distancing and isolation on epidemic spreading modeled via dynamical density functional theory

For preventing the spread of epidemics such as the coronavirus disease COVID-19, social distancing and the isolation of infected persons are crucial. However, existing reaction-diffusion equations for epidemic spreading are incapable of describing these effects. In this work, we present an extended model for disease spread based on combining a susceptible-infected-recovered model with a dynamical density functional theory where social distancing and isolation of infected persons are explicitly taken into account. We show that the model exhibits interesting transient phase separation associated with a reduction of the number of infections, and allows for new insights into the control of pandemics.

Controlling the Microstructure and Phase Behavior of Confined Soft Colloids by Active Interaction Switching

We explore the microstructure and phase behavior of confined soft colloids which can actively switch their interactions at a predefined kinetic rate. For this, we employ a reactive dynamical density-functional theory and study the effect of a two-state switching of the size of colloids interacting with a Gaussian pair potential in the nonequilibrium steady state. The switching rate interpolates between a near-equilibrium binary mixture at low rates and a nonequilibrium monodisperse liquid for large rates, strongly affecting the one-body density profiles, adsorption, and pressure at confining walls. Importantly, we show that sufficiently fast switching impedes the phase separation of an (in equilibrium) unstable liquid, allowing the control of the degree of mixing and condensation and local microstructuring in a cellular confinement by tuning the switching rate.

In Situ Analysis of Weakly Bound Proteins Reveals Molecular Basis of Soft Corona Formation

Few experimental techniques allow the analysis of the protein corona in situ. As a result, little is known on the effects of nanoparticles on weakly bound proteins that form the soft corona. Despite its biological importance, our understanding of the molecular bases driving its formation is limited. Here, we show that hemoglobin can form either a hard or a soft corona on silica nanoparticles depending on the pH conditions. Using cryoTEM and synchrotron-radiation circular dichroism, we show that nanoparticles alter the structure and the stability of weakly bound proteins in situ. Molecular dynamics simulation identified the structural elements driving protein-nanoparticle interaction. Based on thermodynamic analysis, we show that nanoparticles stabilize partially unfolded protein conformations by enthalpy-driven molecular interactions. We suggest that nanoparticles alter weakly bound proteins by shifting the equilibrium toward the unfolded states at physiological temperature. We show that the classical approach based on nanoparticle separation from the biological medium fails to detect destabilization of weakly bound proteins, and therefore cannot be used to fully predict the biological effects of nanomaterials in situ.

Probing the protein corona around charged macromolecules: interpretation of isothermal titration calorimetry by binding models and computer simulations

Isothermal titration calorimetry (ITC) is a widely used tool to experimentally probe the heat signal of the formation of the protein corona around macromolecules or nanoparticles. If an appropriate binding model is applied to the ITC data, the heat of binding and the binding stoichiometry as well as the binding affinity per protein can be quantified and interpreted. However, the binding of the protein to the macromolecule is governed by complex microscopic interactions. In particular, due to the steric and electrostatic protein–protein interactions within the corona as well as cooperative, charge renormalization effects of the total complex, the application of standard (e.g., Langmuir) binding models is questionable and the development of more appropriate binding models is very challenging. Here, we discuss recent developments in the interpretation of the Langmuir model applied to ITC data of protein corona formation, exemplified for the well-defined case of lysozyme coating highly charged dendritic polyglycerol sulfate (dPGS), and demonstrate that meaningful data can be extracted from the fits if properly analyzed. As we show, this is particular useful for the interpretation of ITC data by molecular computer simulations where binding affinities can be calculated but it is often not clear how to consistently compare them with the ITC data. Moreover, we discuss the connection of Langmuir models to continuum binding models (where no discrete binding sites have to be assumed) and their possible extensions toward the inclusion of leading order cooperative electrostatic effects.

Recent advances in stimuli-responsive core-shell microgel particles: synthesis, characterisation, and applications

Inspired by the path followed by Matthias Ballauff over the past 20 years, the development of thermosensitive core-shell microgel structures is reviewed. Different chemical structures, from hard nanoparticle cores to double stimuli-responsive microgels have been devised and successfully implemented by many different groups. Some of the rich variety of these systems is presented, as well as some recent progress in structural analysis of such microstructures by small-angle scattering of neutrons or X-rays, including modelling approaches. In the last part, again following early work by the group of Matthias Ballauff, applications with particular emphasis on incorporation of catalytic nanoparticles inside core-shell structures—stabilising the nanoparticles and granting external control over activity—will be discussed, as well as core-shell microgels at interfaces.

Gold, Silver and Iron Oxide Nanoparticles: Synthesis and Bionanoconjugation Strategies Aimed at Electrochemical Applications

Nanomaterials have revolutionized the sensing and biosensing fields, with the development of more sensitive and selective devices for multiple applications. Gold, silver and iron oxide nanoparticles have played a particularly major role in this development. In this review, we provide a general overview of the synthesis and characteristics of gold, silver and iron oxide nanoparticles, along with the main strategies for their surface functionalization with ligands and biomolecules. Finally, different architectures suitable for electrochemical applications are reviewed, as well as their main fabrication procedures. We conclude with some considerations from the authors' perspective regarding the promising use of these materials and the challenges to be faced in the near future.

Understanding the relevance of protein corona in nanoparticle-based therapeutics and diagnostics

Over the past few decades, nanoparticle-based therapeutic and diagnostic systems have gained immense recognition. A relative improvement in the status of the global cancer burden has been successful due to the advent of nanoparticle-based formulations. However, exposure of nanoparticles (NPs) to a real-time biological media alters its native identity due to the formation of the biomolecular corona. Such biological interactions hinder the efficiency of the NPs system. The parameters that govern such intricate interaction are generally overlooked while designing nano drugs and delivery systems (nano-DDS). Fabricating nano-DDS with prolonged circulation time, enhanced drug-loading, and release capacity along with efficient clearance, remain the primary concerns associated with cancer therapeutics. This present review firstly aims to summarize the critical aspects that influence protein coronation on therapeutic nanoparticles designed for anti-cancer therapy. The role of protein corona in modifying the overall pharmacodynamics of the nanoparticle-based DDS has been discussed. Further, the studies and patents that extend the concept of protein corona into diagnostics have been elaborated. An understanding of the pros and cons associated with protein coronation would not only help us gain better insights into the fabrication of effective anti-cancer drug-delivery systems but also improve the shortcomings related to the clinical translation of these nanotherapeutics.

Protein corona and its applications.

Analysis of temporally evolved nanoparticle-protein corona highlighted the potential ability of gold nanoparticles to stably interact with proteins and influence the major biochemical pathways in Brassica juncea

Nanoparticles (NPs) are known to adsorb proteins from their surroundings, forming NP-protein corona, which determines their fate, distribution, and effects, yet no information of protein corona (PC) has been gathered in the plants so far. Here we report, the analysis of temporally evolved (2 h-36 h) AuNP-protein coronas formed with Brassica juncea leaf crude protein & nuclear-enriched fraction. Protein coronas were characterized by the techniques including SDS PAGE (Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis), spectrophotometry, dynamic light scattering, zeta potential measurements, and Nano LC-MS/MS. Data analysis revealed the formation of two regimes (Regime I from 2 to 8 h & regime II from 16 to 36 h). Interestingly, coated AuNPs had approx. 30% higher zeta potential than pristine AuNPs after 36 h of interactions. The increase in hydrodynamic radii and adsorbed protein concentrations were consistent with the evolution of zeta potential, indicating the probable role of proteins in providing the better stability of AuNPs. MS analysis identified 97 proteins from regime I (soft corona) and 181 proteins from regime II (hard corona) of crude PC. On the other hand, 282 and 308 proteins were identified from nuclear soft and hard corona respectively, indicating better affinity of nuclear proteins. Besides, the high-affinity proteins (fold change ≥5) were found to be rich in lysine residues showing their involvement in promoting the adsorption. Notably, 27% of regime II corona proteins of the crude protein fraction were from energy-yielding pathways highlighting the potential ability AuNPs to influence the yield in Brassica juncea.

Multiscale Molecular Dynamics Simulation of Multiple Protein Adsorption on Gold Nanoparticles

A multiscale molecular dynamics simulation study has been carried out in order to provide in-depth information on the adsorption of hemoglobin, myoglobin, and trypsin over citrate-capped AuNPs of 15 nm diameter. In particular, determinants for single proteins adsorption and simultaneous adsorption of the three types of proteins considered have been studied by Coarse-Grained and Meso-Scale molecular simulations, respectively. The results, discussed in the light of the controversial experimental data reported in the current experimental literature, have provided a detailed description of the (i) recognition process, (ii) number of proteins involved in the early stages of corona formation, (iii) protein competition for AuNP adsorption, (iv) interaction modalities between AuNP and protein binding sites, and (v) protein structural preservation and alteration.

Electrical Potential Specified Release of BSA/Hep/Polypyrrole Composite Film and Its Cellular Responses

A facile strategy is needed for accurate time-space supply of suitable growth factors or drugs. Polypyrrole (PPy) was able to carry almost all kinds of negatively charged biomolecules through anodizing method, which made it an appropriate way for codeposition of multiple molecules. The difference in the conjugation between different molecules and PPy makes it possible for selective release when the redox state of PPy changes. In this work, bovine serum albumin (BSA) and heparin (Hep) were chosen to be the model molecules in view of their differences in the level of electronegativity and molecular weight. Double-layer deposition method was used to improve the biocompatibility of PPy/BSA/Hep film. It was found the content of BSA and Hep in the film can be controlled by regulating deposition current and time. BSA release was facilitated under positive voltage and then promote the proliferation of preosteoblasts, while Hep release was promoted under negative voltage and enhance cell differentiation. Our work provides a dual-molecule model in PPy for selective release and further explores the mechanism of release selectivity, this discovery has potential applications in tissue engineering and regenerative medicine.

Interaction of Proteins with Polyelectrolytes: Comparison of Theory to Experiment

We discuss recent investigations of the interaction of polyelectrolytes with proteins. In particular, we review our recent studies on the interaction of simple proteins such as human serum albumin (HSA) and lysozyme with linear polyelectrolytes, charged dendrimers, charged networks, and polyelectrolyte brushes. In all cases discussed here, we combined experimental work with molecular dynamics (MD) simulations and mean-field theories. In particular, isothermal titration calorimetry (ITC) has been employed to obtain the respective binding constants K_b and the Gibbs free energy of binding. MD simulations with explicit counterions but implicit water demonstrate that counterion release is the main driving force for the binding of proteins to strongly charged polyelectrolytes: patches of positive charges located on the surface of the protein become multivalent counterions of the polyelectrolyte, thereby releasing a number of counterions condensed on the polyelectrolyte. The binding Gibbs free energy due to counterion release is predicted to scale with the logarithm of the salt concentration in the system, which is verified by both simulations and experiment. In several cases, namely, for the interaction of proteins with linear polyelectrolytes and highly charged hydrophilic dendrimers, the binding constant could be calculated from simulations to very good approximation. This finding demonstrated that in these cases explicit hydration effects do not contribute to the Gibbs free energy of binding. The Gibbs free energy can also be used to predict the kinetics of protein uptake by microgels for a given system by applying dynamic density functional theory. The entire discussion demonstrates that the direct comparison of theory with experiments can lead to a full understanding of the interaction of proteins with charged polymers. Possible implications for applications, such as drug design, are discussed.

Global diffusion limitations during the initial phase of the formation of a protein corona around nanoparticles

Herein, I illustrate analytically how the global diffusion limitations can influence the first phase of the protein-corona formation at nanoparticles under conditions of intravascular injection. In particular, the concentrations of proteins near the boundaries of the injection region are shown to be comparable with those far from the region. In contrast, the concentrations of proteins inside the injection region may be dramatically smaller than those outside, and the ratio of these two concentrations for proteins of different size may be much higher, by a few orders of magnitude, for smaller proteins. These differences in the spatial distribution of proteins are expected to play a key role in the Vroman effect at the onset of the protein-corona formation.

Nonequilibrium Uptake Kinetics of Molecular Cargo into Hollow Hydrogels Tuned by Electrosteric Interactions

Hollow hydrogels represent excellent nano- and microcarriers due to their ability to encapsulate and release large amounts of cargo molecules (cosolutes) such as reactants, drugs, and proteins. In this work, we use a combination of a phenomenological effective cosolute-hydrogel interaction potential and dynamic density functional theory to investigate the full nonequilibrium encapsulation kinetics of charged and dipolar cosolutes by an isolated charged hollow hydrogel immersed in a 1:1 electrolyte aqueous solution. Our analysis covers a broad spectrum of cosolute valences ( z_c) and electric dipole moments (μ_c), as well as hydrogel swelling states and hydrogel charge densities. Our calculations show that, close to the collapsed state, the polar cosolutes are predominantly precluded and the encapsulation process is strongly hindered by the excluded-volume interaction exerted by the polymer network. Different equilibrium and kinetic sorption regimes (interface versus interior) are found depending on the value and sign of z_c and the value of μ_c. For cosolutes of the same sign of charge as the gel, the superposition of steric and electrostatic repulsion leads to an "interaction-controlled" encapsulation process, in which the characteristic time to fill the empty core of the hydrogel grows exponentially with z_c. On the other hand, for cosolutes oppositely charged to the gel, we find a "diffusion-controlled" kinetic regime, where cosolutes tend to rapidly absorb into the hydrogel membrane and the encapsulation rate depends only on the cosolute diffusion time across the membrane. Finally, we find that increasing μ_c promotes the appearance of metastable and stable surface adsorption states. For large enough μ_c, the kinetics enters an "adsorption-hindered diffusion", where the enhanced surface adsorption imposes a barrier and slows down the uptake. Our study represents the first attempt to systematically describe how the swelling state of the hydrogel and other leading physical interaction parameters determine the encapsulation kinetics and the final equilibrium distribution of polar molecular cargo.